This invention relates generally to ion sputtering devices, and more particularly to an improved apparatus and method for ion sputtering which are more efficient than the prior art devices and methods, and further which are capable of coating hard to reach places, such as the interior surfaces of pipes with small diameters, or interior surfaces of openings or holes.
Methods of ion sputtering utilizing glow discharge, and devices for carrying out these methods are well-known in the art. For example, U.S. Pat. No. 4,221,652 to Kuriyama, U.S. Pat. No. 4,376,025 to Zega, U.S. Pat. No. 4,395,323 to Denton et al., U.S. Pat. No. 4,412,906 to Sato et al., U.S. Pat. No. 4,895,631 to Wirz et al., U.S. Pat. No. 4,946,576 to Dietrich et al., U.S. Pat. No. 4,965,248 to Poppe et al., U.S. Pat. No. 4,988,422 to Wirz, U.S. Pat. No. 5,069,770 to Glocker, U.S. Pat. No. 5,317,006 to Kumar, U.S. Pat. No. 5,338,425 to Mishima et al., and U.S. Pat. No. 5,346,601 to Barada et al. are representative of the available prior art. Typically, such apparatuses include two electrodes, namely a cathode target of metallic or metallic alloy material which is to be deposited, such as a precious metal or precious metal alloy, and an anode which is located in spaced relation to the cathode. The electrodes are placed in a vacuum chamber which is pumped out continuously, and plasma forming gas is fed into the chamber. For flat or planar surfaces which are to be coated, planar cathode targets are used. Similarly, when the inner surface of a cylinder is to be coated, the cathode target is a rod which is disposed along an axis of the cylinder within the cylinder.
It has been found that each of the prior art devices suffers from the disadvantage of being inefficient in that a significant amount of sputtered material is not directed to the surface of the substrate to be coated. The sputtered material which does not deposit onto the substrate to be coated is evacuated from the chamber and is wasted. Another shortcoming of the prior art devices is that they are limited to a low current density on the cathode target of approximately ten to twenty amps per square meter. It has been found that when the pressure of the plasma forming gas is increased, the current density is also increased. However, when the current density and gas pressure increase in the prior art devices, a phenomenon known as "back sputtering" occurs in which the sputtered atoms travel back towards the cathode target.
One known solution to the operating disadvantages of the prior art is to use a high-efficiency magnetron sputtering device in which a magnetic system capable of generating a magnetic field is mounted on a side opposite to the target surface of the cathode. As a result of the interaction of the magnetic field and the electric field above the erosion zone of the cathode target surface, a localized tunnel zone of the working plasma with high ionization degree is formed. This generates relatively high current density on the cathode target, e.g., up to approximately 3000 amps per square meter.
Magnetron sputtering devices are widely used in the industry due to their high productivity, relative simplicity, and reliability. However, such devices are incapable of coating the inner surfaces of pipes and inner surfaces of holes having small diameters. The minimum possible diameters of pipes and holes that can be coated using magnetron sputtering devices is approximately fifty millimeters.
A sputtering deposition apparatus 10 illustrated in FIG. 1 represents one known technology developed to overcome many of these and other shortcomings of the prior art. In this apparatus, which is disclosed in Ukraine Patent No. 7111 to Dudko et al., there is provided an anode 12 and nozzle 14 disposed above a cathode target 16. The anode 12 is insulated from the nozzle 14 by a sleeve 15 of dielectric material. The arrangement is such that the nozzle 14 is directed towards the cathode target 16 along an axis A generally perpendicular to the plane of the cathode target 16. A substrate 18 to be coated lies along a plane generally perpendicular to the plane of the cathode target 16 and parallel to the axis A of the nozzle 14. A supply of plasma forming gas (see arrows 20), such as argon, is directed through the tip of the nozzle 14 toward the cathode target 16. An electric field (not shown) generated by the anode 12 and cathode target 16 within the gas flow 20 is effective to ionize the gas and form an ionized gas cloud (broken lines) 21 adjacent to the surface of the cathode target 16. High energy ions 22 within the gas cloud 21 bombard the surface of the cathode target 16 (see arrows 23) and cause individual atoms 24, or blocks of atoms of the cathode target material, to be stripped away from the cathode target 16. The individual stripped atoms 24 are not directed in any particular direction, but instead travel away from the cathode target in random directions, only some of which are directed toward the substrate 18 to be coated (see arrow 25). While this device is effective for its intended purpose, it has been found that many of the stripped atoms 24 never contact the substrate to be coated, and therefore there is still a significant amount of waste associated with this device.